The present disclosure relates to technology for non-volatile storage.
One type of non-volatile storage is semiconductor memory. For example, non-volatile semiconductor memory is used in solid state drives, mobile computing devices, non-mobile computing devices and other non-volatile memory systems. Typically, the non-volatile memory system has a memory controller which controls access of a host system to non-volatile memory in memory system. The host system could be computer system, cellular telephone, server, etc. The non-volatile memory system and host system may exchange data over, for example, a Peripheral Computer Interface Express (PCIe) bus. Non-volatile Memory Express (NVMe) is a logical device interface specification for accessing non-volatile storage attached via a PCIe bus. NVMe takes advantage of parallelism offered by semiconductor memory such as, but not limited to, solid state drives.
The memory controller will typically have some amount of volatile memory, which it may use for a variety of tasks. For example, the volatile memory can be used to cache a portion of a management table that is used to translate between logical addresses used by the host system and physical addresses in the non-volatile memory. Note that a full version of the management table may be stored in the non-volatile memory. A benefit of caching the management table is that when the memory system receives a read or write request, it can determine which memory location needs to be accessed based on a much quicker lookup in the memory controller's volatile memory. For fast consistent performance, the organization of the management table may be chosen to minimize the amount of computation and number of volatile memory lookups required at the expense of requiring more volatile memory. The memory controller may use the volatile memory for other purposes.
In some memory access protocols, the host system may make a portion of its host memory available for the exclusive use of the memory controller. For example, some versions of the NVMe protocol allow a Host Memory Buffer (HMB) option in which a portion of the host memory is allocated for the exclusive use of the memory controller. This option can save cost by allowing the memory controller to have less volatile memory.